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NEW YORK (MedscapeWire) May 06 — Growth hormone (GH) response to maximal exercise is impaired in patients with fibromyalgia, according to research reported in the May issue of Arthritis & Rheumatism. Normalization with pyridostigmine pretreatment suggests a defect in somatostatin tone, which may be related to the exhaustive stage of chronic stress.

“The results of this study indicate that GH deficiency is probably more common in fibromyalgia patients than was originally reported,” senior author Robert Bennett, MD, MRCP, from Oregon Health Sciences University in Portland, says in a news release.

Fibromyalgia is thought to be a stress-related syndrome, linked to malfunctions of the hypothalamic, pituitary, and adrenal hormones, including GH.

In this study, 20 women with fibromyalgia and a control group of 10 healthy women exercised to volitional exhaustion, reaching maximum respiratory and pulse rate on a treadmill. One month later, testing was repeated 1 hour after pretreatment with pyridostigmine, which inhibits somatostatin secretion.

Without pyridostigmine pretreatment, 11 of the 20 patients with fibromyalgia had no exercise-induced increase in GH levels. After the administration of pyridostigmine, 19 of the 20 patients had a normal GH response to exercise.

The overall increase in GH was 8 times higher than without pretreatment and was similar to that seen in controls. Pyridostigmine alone did not stimulate GH secretion in patients with fibromyalgia, nor did it affect GH levels in controls. Even those fibromyalgia patients with normal insulin-like growth factor 1 levels had an impaired GH response to exercise.

“Recognition of defective GH secretion in fibromyalgia patients is of some practical relevance because GH replacement therapy was shown to benefit fibromyalgia patients in a 9-month placebo-controlled study,” Bennett says.